Caramel croquembouche

Bring 180 ml water, butter, salt and 15 g sugar to the boil. Remove from the heat and add the flour at once. Mix, then stir over gentle heat for about 1 minute to dry the paste. Cool slightly. Beat 3 whole eggs and gradually mix in until smooth. Transfer to a piping bag and chill for 60 minutes.

While the pastry rests, separate the remaining eggs and keep their yolks. Split the vanilla and scrape out the seeds. Heat the milk with pod and seeds. Whisk the yolks with 80 g sugar, then the cornstarch. Whisk in the strained hot milk. Return to the pan and stir until thick with the first bubbles. Spread in a shallow dish, cover the surface and cool for about 20 minutes. Refrigerate until fully cold.

Heat the oven to 180 °C. Pipe small, even choux spaced apart on a silicone-lined tray. Bake for about 30 minutes without opening until risen, golden and firm. Cool on a rack for about 30 minutes. Whisk the cold custard until smooth, make holes underneath the choux and pipe in the filling.

Squeeze the lemon and measure 5 ml juice. Heat the remaining 300 g sugar and 100 ml water with this juice to a light amber caramel. Remove from the heat. Hold the choux with tongs, carefully dip their tops in caramel and let set on a silicone mat. Dip one side of each into the still-fluid caramel and assemble a stable ring, then progressively smaller rings into a small dome. Briefly hold each in place without touching hot caramel. Set for about 15 minutes.